Typically, in order to solve mathematical equations using calculating devices, it has been first necessary for a user of a calculating device to manipulate or reduce an equation or in some other way conform to a lengthy, often difficult means to prepare an equation before solving the equation using the calculating device. For these reasons, often the amount of effort, such as the number of key strokes required by a user to perform useful functions on a calculator, has been excessive.
There have been efforts to make calculating devices more friendly to users. For instance, one prior art solution allowed for the permanent assigning of keys to variables in a single mathematical equation. See General Purpose Calculator With Capability For Performing Interdisciplinary Business Calculations, Rodes et al., U.S. Patent Ser. No. 3,863,060, which is hereby incorporated by reference. Although the interface in Rodes et al. was efficient to use, there was no flexibility in the choice of mathematical equation. If more such equations were added to a calculating device severe problems with key density on the calculating device could result.